drm: drop uapi dependency from drm_vblank.h

drm_vblank.h included uapi/drm/drm.h.
It turns out this include was not required - delete it.

Note: uapi/drm/drm.h is included indirect via drm_file.h,
but there are no dependencies in drm_vblank.h so the removal
is legit.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Sean Paul <sean@poorly.run>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Stefan Agner <stefan@agner.ch>
Cc: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190718161507.2047-4-sam@ravnborg.org